Transdermal medical devices, including vascular catheters, have become essential in the management of hospitalized or chronically ill patients. Unfortunately, vascular catheters have become the major source for hospital-acquired sepsis. Hence, the benefit derived from transdermal medical devices such as vascular catheters is often upset by infectious complications. Thrombotic occlusions of the lumen of central venous catheters (“CVC”) are another complication that will often lead to the removal of catheters.
To reduce problems associated with thrombus formation, it is now common to “lock” intravascular access catheters between successive uses. Locking typically involves first flushing the catheter with saline to remove blood, medications, cellular debris and other substances from the catheter lumen. After the catheter has been flushed, a locking solution, typically heparin, is then injected to displace the saline and fill the lumen. The heparin locking solution both excludes blood from the lumen and actively inhibits clotting and thrombus formation within the lumen. To address infection, various antimicrobial substances have been combined with the locking solution in order to inhibit infection at the same time that thrombosis is being inhibited. However, problems with current and continuously emerging resistance to antimicrobial substances, as well as the over-use (and hence the increased risk of developing resistance) of antimicrobials, is an ever-growing concern.
Staphylococcus epidermidis and S. aureus account for 75% of CVC related infections. Candida species account for another 10% to 15% of such infections. The use of antistaphylococcal antibiotics to prevent these infections has been found to reduce CVC related bacterial infections, but only at the expense of the occurrence of higher rates of fungal (Candida) infections. The fibrous glycocalyx material produced by Staphylococci and Candida helps these organisms adhere and stick to catheter surfaces. These microbiological biofilm layers are made of fibrous glycocalyx material primarily polysaccharide in nature. The protective sheath provided by the glycocalyx at the infected site effectively prevents the elimination and treatment of these infections. As a result, microbial growth inhibiting solutions are needed that are effective for reducing or eliminating glycocalyx of infectious microorganisms typically associated with catheter colonization and infection.
Transdermal vascular catheters get engulfed by a fibrin sheath that subsequently acts to cover the internal and external surfaces of a catheter. This fibrin sheath provides such organisms as Staphylococci and Candida, with an enhanced adherence capacity to the catheter surface. Unlike these particular microbes, gram-negative bacilli do not adhere well to fibrin and fibronectin. A composition that halts fibrin formation would thus be particularly useful in halting the colonization of Staphylococci, Candida, and the like, at transdermal catheter sites.
Ethylenediaminetetraacetic acid (“EDTA”) is an anticoagulant used in blood collection tubes. It is also recognized as a calcium chelating agent. EDTA is also recognized to have an antibacterial and antistaphylococcal effect (alone or in combination) (Harper & Epis (1987) Microbios. 51:107; Said et al. (1987) J. Med. Microbiol. 24:267; Root et al. (1988) Antimicrob. Agents Chemother. 32:1627). While those investigators found EDTA to be bacteriocidal, no remedy or suggestion of how the microbial glycocalyx of a device-related infection could be eliminated was provided.
Ethylene glycol tetraacetic acid (“EGTA”) is another recognized chelating agent. This agent has not been described as antimicrobial. Triethylene tetramine dihydrochloride (trientine 2HCl) (“TTH”) is a recognized chelating agent that chelates copper. TTH and other chelating agents, including diethylenetriamine pentaacetic acid (“DTPA”), are similarly not recognized as having antimicrobial activity.
Although glycopeptide antibiotics (vancomycin and teicoplanin) are effective against staphylococci in vitro and in tissue, they are not active against adherent staphylococci embedded in a biofilm layer, such as glycocalyx. While flushing with such agents may acutely destroy these microorganisms, the risk of rapid development of tolerant and resistant strains in the patient being treated makes this a contraindicated procedure in most cases.
U.S. Pat. No. 5,362,754 to Raad (“Raad I”) describes compositions for use with catheters that include a tetracycline antibiotic, such as minocycline, and EDTA. Raad I teaches the use of 10-100 mg/ml of EDTA in combination with 0.001-100 mg/ml of minocycline and the more preferred combination of 20-60 mg/ml of EDTA and 2-9 mg/ml of minocycline. U.S. Pat. No. 5,688,516 also to Raad (“Raad II”) in Example 10 teaches that minocycline and EDTA compositions of less than 3 mg/ml EDTA are ineffective at controlling all microbial growth. Raad II further teaches: “These studies also demonstrate the marked enhancement of anti-Candida albicans inhibitory activity where a ratio of minocycline to EDTA of 10:1 (10% EDTA) is used.”
U.S. Pat. Nos. 4,343,788 and 4,479,795 to R. V. Mustacich describe polymer compositions containing carboxylate antimicrobial agents for incorporation into catheters. U.S. Pat. No. 4,392,848 to D. S. Lucas describes polymer compositions for incorporation into catheters that are permeable to carboxylate antimicrobial agents. U.S. Pat. No. 4,489,097 to R. L. Stone (“Stone”) describes intravenous solutions containing carboxylate antimicrobial agents, preferably n-hexanoic and n-octanoic acids and pharmaceutically-acceptable, water-soluble salts thereof. Stone teaches the use of these carboxylate antimicrobial agents to sterilize intravenous solutions and to maintain these intravenous solutions sterile during manipulation. Administration of Stone's solutions as described into an intravenous catheter to “lock” the catheter under a static (no flow) situation would result in rapid occlusion of the access due to backflow of blood into the device and the lack of anticoagulation characteristics of the described compositions.
A prophylactic agent for catheter maintenance should both inhibit/eliminate the formation of polysaccharide-rich glycocalyx and eliminate Staphylococci and fungi. In view of the foregoing, there is a need for improved compositions, kits and methods for flushing, locking and disinfecting catheters. Such compositions should have antimicrobial activity against a broad spectrum of microorganisms, preferably including fungi and both gram-positive and gram-negative bacteria, and preferably be effective against planktonic (free-floating) and adherent microorganisms embedded in a biofilm. The compositions should discourage the development of resistant microbes, be relatively inexpensive, non-toxic, compatible with the catheter material, safe if inadvertently infused systemically, easy to implement, require minimum or no solution, and be useful with most or all types of implanted catheters, including hemodialysis and hemofiltration catheters, IV catheters, peritoneal dialysis catheters, urinary catheters, chemotherapy catheters, and the like. At least some of these objectives are met by embodiments of the invention described hereinafter.